Apparatus for measuring paper stock consistency

ABSTRACT

A densitometer for paper stock has a wide, vertical metal pipe with a central inlet. Two restricted nozzles in the pipe are equidistant from the inlet in opposite vertical directions and connected to the two leg ends of an inverted U-tube by narrow copper tubes soldered to the outside of the wide tube and to each other for heat transfer. A pump drives the measured stock through the inlet and from both ends of the pipe through a common outlet restricted to maintain high pressure in the system. The copper tubing is supplied with respective streams of the liquid in the stock at a very slow rate by means of a second pump and a filter which removes the fibers from the pumped liquid.

United States Patent [191 Fajans et a1.

[ Mar. 11,1975

[ APPARATUS FOR MEASURING PAPER STOCK CONSISTENCY [75] Inventors: Jack Fajans, Teaneck; John E.

Nankivell, Florham Park, both of [21} Appl. No.: 410,755

3,802,964 4/1974 Forgacs et al. 162/198 FOREIGN PATENTS OR APPLICATIONS 160,353 3/1964 U.S.S.R 73/438 Primary Examiner-Richard C. Queisser Assistant Examiner-Stephen A. Kreitman Attorney, Agent. or FirmHans Berman [57] ABSTRACT A densitometer for paper stock has a wide, vertical metal pipe with a central inlet. Two restricted nozzles in the pipe are equidistant from the inlet in opposite vertical directions and connected to the two leg ends of an inverted U-tube by narrow copper tubes soldered to the outside of the wide tube and to each other for heat transfer. A pump drives the measured stock through the inlet and from both ends of the pipe through a common outlet restricted to maintain high pressure in the system. The copper tubing is supplied with respective streams of the liquid in the stock at a very slow rate by means of a second pump and a filter which removes the fibers from the pumped liquid.

4 Claims, 1 Drawing Figure APPARATUS FOR MEASURING PAPER STOCK CONSISTENCY This invention relates to specific gravity measure ment, and particularly to a device for precisely measuring the specific gravity of a suspension of solids in a continuous liquid phase. In its more specific aspects, the invention is concerned with an improvement of the apparatus disclosed in U.S. Pat. No. 3,473,401 which measures the consistency of aqueous paper stock by determining the specific gravity of the stock.

The apparatus of the patent compares the specific gravity of a stock solution with that ofa standard liquid, more specifically water, and has been used successfully where the sole variable in the stock is the concentration of fiber particles. Because of the relatively small difference in specific gravity between the solid and liquid phases in the paper stock, it has been found that the readings obtained by the known device are not suffi ciently accurate if the concentration of solutes in the aqueous phase of the stock and the specific gravity of the stock vary in a manner not infrequently encountered in paper manufacturing.

The object of the invention is an improvement in the earlier device which compensates automatically for changes in the specific gravity ofthe liquid phase in the paper stock, and thereby improves the reproducibility of stock consistency readings.

According to the present invention, this is achieved by replacing water as a reference liquid in the apparatus by streams of the liquid phase in the stock which are separated from the fibers by filtering and slowly pumped through the conduit system for the reference liquid.

Other features and the attendant advantages of the improved consistency measuring apparatus of this invention will readily become apparent from the following detailed description of a preferred embodiment when considered in connection with the appended drawing.

The sole FIGURE of the drawing shows a consistency measuring apparatus of the invention in fragmentary elevation, and partly in section.

The main container. of the device is assembled from standard galvanized 2 inches steel pipes and corresponding T-fittings in the shape of a vertically elon gated rectangle. The two vertical legs 1, 2 of the rectangle are connected by transverse pipe sections 3, 4 near the plugged top and bottom ends of the legs 1, 2. Two lengths 5, 6 of A inch copper tubing extend longitudinally into the top and bottom of the leg 1 through the respective plugs and past the orifices of the transverse sections 3, 4. Their ends are longitudinally closed and provided with radial bores 7, 7' to form restricted nozzles for horizontal fluid flow between the leg 1 and the copper tubing.

T-fittings 8, 9 are arranged in the legs 1, 2 to form an inlet in the leg 1 which is centered between the nozzles 7, 7' and an outlet in the leg 2 on the same level as the inlet 8. A discharge pipe 10 connected with the outlet 9 has a long section 11 of A inch internal diameter, the purpose of which will presently become apparent, and a shut-off valve 12.

The inlet 8 is connected with a stock tank 14 by a pump 13. The pump, not shown in detail, is a screw pump of the type illustrated in Perrys Chemical Engineers Handbook, 4th ed., page 6-l2 (Moyno pump).

,Vertical portions of the copper tubes 5, 6 are soldered to the outer surface of the leg 1. The tubes extend toward each other, thereafter in respective coil turns 5, 6' soldered to the outer surface of the leg I and/or the T-fitting 8, and then horizontally away from the container. Their ends are bent upward and connected by an inverted U-tube 20 of glass. Two valves 16, 17 are provided in each horizontal run of the tubes 5, 6, and side tubes 18 on the horizontal runs between the valves 16, 17 are equipped with valves 19. The horizontal runs and coil turns of copper tubing are soldered to each other. Their ends near the U-tube 20 are connected by a valve 21. A valve 23 normally closes a filling nipple on the U-tube 20.

Feeding tubes 24 of copper having an internal diam eter of about A inch connect the two valves 19 to a second pump 25 which draws a stream of the stock suspension from the outlet pipe 11 at a rate of about one liter per hour through a filter 26, and discharges respective part streams of the filtered, pumped liquid through the feeding tubes into the vertical lengths 5, 6 of copper tubing and out of the nozzles 7, 7.

In normal operation of the apparatus described, paper stock fills the pump 13, the main container and the connecting pipes and valves. It is in pressuretransmitting contact at the nozzles 7, 7' with liquid which fills the two copper tubes 5, 6 to respective interfaces 22 with a body of ethylbenzene in the bight portion of the U-tube 20.

The flow resistance of the pipe section 11 and the rate of delivery of the pump 13 are selected in such a manner as to maintain a pressure of about pounds per square inch in the liquid filled apparatus when the valves 12, 16, 17, 19 are open and all other valves are closed. The solder joints, not visible in the drawing, which connect the vertical portions of the copper tubes 5, 6 and the coil turns 5, 6' to the steel pipe and T- fittings of the leg 1, and which connect the horizontal runs of copper tubing to each other are so heavy that heat exchange between the fluids prevents temperature differences of more than O.5F in the conduits which are connected by the solder.

The stream of stock which enters the main container through the inlet 8 is divided into two equal branches which flow in opposite directions in the legs 1, 2 and are ultimately jointly discharged through the outlet 9 and the restricted tubing section 11. The frictional effects in the two branches of the stock stream balance each other. The high pressure maintained in the apparatus favors the dissolution of air bubbles introduced with the stock, or at least their compression to an insignificant volume.

The vertical spacing ofthe inlet 8 from the horizontal runs of the copper tubes 5, 6 has been enlarged in the drawing for the sake of clearer pictorial representation. it is preferably of negligible magnitude as compared to the spacing of the nozzles 7, 7' which is about ten feet.

The interfaces 22 are on a common level if the main container is filled with a liquid having the same specific gravity as the liquid which fills the copper tubes 5, 6, and the drawing illustrates the interfaces 22 in this condition of the apparatus. it can readily be calculated that the vertical spacing of the two interfaces 22 in the illustrated apparatus is about 3.5 centimeters when the main container is filled with paper stock consisting of water and 0.5 percent cellulose while the copper tubing is filled with water. A change in consistency by 0.0! percent cellulose (2 percent) results in a change of about 0.07 centimeters which can readily be read with a magnifying glass, and even more. precisely with a cathetometer. The combined effects of temperature variation, residual gas bubbles, and internal friction in the flowing liquid are substantially smaller.

Because of the sensitivity of the differential pressure indicator 20, the pump 22 is preferably chosen so as to operate intermittently, for example, a piston pump delivering one pressure stroke per 30 seconds, but a continuously operating pump, such as a gear pump, is also useful. The filter may be of the cartridge clarifier type (Perrys Chemical Engineers Handbook, 4th ed., FIG. 19-134), the cartridge or cartridges being replaced from time to time for removal of accumulated fibers.

The composition of the reference liquid in horizontal portions of the conduit system has little influence on the readings produced by the indicator 20, but it is essential that the composition in the vertical lengths of copper tubing 5, 6 be closely similar to or identical with the composition of the liquid phase in the measured stock, and this is achieved adequately by pumping filtered stock through the tubing and out of the nozzles 7, 7, thereby also preventing entry of stock from the container into the nozzles by diffusion. The flow rate in the two vertical copper tubes 5, 6 is balanced by means of the two valves 19.

Although the flow velocity in the copper tubing 5, 6 is extremely low, it has been found that the desired thermal equilibrium between the stock in the main container and the reference liquid in the copperconduits is disturbed sufficiently by the movement of the liquid to require faster heat exchange between the two liquids than is available from the lengths of vertical copper tubing soldered to the outer face of the container leg 1. The copper tubes 5, 6, therefore, are each coiled in at least one horizontal turn 6' about the leg 1 and/or the coaxial portion of the T-fitting 8 so that the flowing reference liquid is at the same temperature as the flowing stock in the apparatus when the reference liquid enters the vertical lengths of copper tubing 5, 6.

The mode of operation of the improved apparatus does not significantly differ from that of the earlier device described in the afore-mentioned patent. The results achieved with stock varying in the composition of its liquid phase are as good as those described in the patent for stock of uniform liquid composition.

Obviously, many variations and modifications of the aforedescribed illustrated apparatus are possible without losing the major benefits of this invention. It is not necessary, for example, to connect the two transverse pipe sections 3, 4 with a second longitudinal leg 2 and a common outlet 9, if maximum accuracy is not required. The pipe sections 3, 4 may serve as separate outlets of the apparatus and may discharge the paper stock through respective throttling devices corresponding to the tubing section 11.

The illustrated U-tube may be replaced by a different set of communicating, tubular, vertically extending legs, and it will be understood that the term U-tube is intended to cover such variations. Ethylbenzene has been found to be a very desirable filling for the U-tube because of the difference between its specific gravity and that of water, and because of the mutual insolubil- 4 ity of thes'eliquids at ordinary atmospheric temperatures, but castor oil and the like may also be used.

It has been found that a single pump 25 connected with a branched conduit 24 and individual valves 19 in the branches can provide two streams of filtered liquid at the same flow rate, but a proportionating pump separately drawing two streams of liquid from the filter 26 and delivering separate pulsed streams of the liquid to the two valves 19 respectively is equally applicable.

The differential pressure indicator 20 has been shown to communicate with the feed pipes 24 upstream from the coil turns 5, 6, but this is not essential, and the connection may be made, for example, at the contiguous, terminal parts of the vertical portions of the copper tubing 5, 6 where the vertical portions are joined to the coil turns 5, 6, the latter actually constituting sections of the feeding tubes 24. Depending on the temperature difference between the measured stock in the leg 1 and the ambient atmosphere, the sections 5', 6-may be coiled about the container in more than one turn.

Various other modifications are contemplated and may obviously be resorted to without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. In an apparatus for measuring'the specific gravity of a suspension of a solid in a continuous liquid phase as a measure of the concentration of said solid in said suspension, the apparatus including a container having an inlet and two outlets communicating with the ambient atmosphere; two restricted nozzles vertically spaced in said container from said inlet in opposite vertical directions in the normal operating condition of the apparatus, said outlets being spaced from respective ones of said nozzles in a direction away from said inlet; a source of said suspension; first pump means for driving said suspension from said source into said container through said inlet and out of said container through said outlets; pressure holding means for holding the pressure of said suspension between said nozzles at least ten pounds per square inch higher than the pressure of said atmosphere when said suspension is driven into said container by said pump means; two conduits respectively communicating with said nozzles and having respective portions spaced from said nozzles; and differential pressure indicating means for indicating the difference of liquid pressure in said portions of said conduits, the improvement which comprises:

a. second pump means communicating with said source and with each of said conduits for withdrawing a stream of said suspension from said source and for feeding respective parts of said stream to said conduits under a pressure sufficient to cause flow of said parts in said conduits and outward of said nozzles into said container; and

b. filter means arranged in series with said second pump means between said source and said conduits for removing said solid from said stream before said parts are fed to said conduits.

2. In an apparatus as set forth in claim 1, each of said conduits having a vertical portion, said portions jointly extending over substantially the entire vertical spacing of said nozzles and being connected to a vertically coextensive portion of said container for heat exchange between fluid in said conduit portions and corresponding portions of said suspension in said container. feed- 6 ing tubes connecting said second pump means to retainer being tubular, and said sections of said feeding SPECUVe comlguous Parts of Sald Conduit P tubes being coiled about said tubular container.

tions, said feeding tubes respectively having sections 4. In an apparatus as set forth in claim 3, each ofsaid extending from said parts horizontally in heat transmttf b b d b b l ting engagement with said container toward said secs ee mg tu es emg e 3 out Sm u comumr 0nd pump means. in at least one turn.

3. In an apparatus as set forth in claim 2, said con 

1. In an apparatus for measuring the specific gravity of a suspension of a solid in a continuous liquid phase as a measure of the concentration of said solid in said suspension, the apparatus including a container having an inlet and two outlets communicating with the ambient atmosphere; two restricted nozzles vertically spaced in said container from said inlet in opposite vertical directions in the normal operating condition of the apparatus, said outlets being spaced from respective ones of said nozzles in a direction away from said inlet; a source of said suspension; first pump means for driving said suspension from said source into said container through said inlet and out of said container through said outlets; pressure holding means for holding the pressure of said suspension between said nozzles at least ten pounds per square inch higher than the pressure of said atmosphere when said suspension is driven into said container by said pump means; two conduits respectively communicating with said nozzles and having respective portions spaced from said nozzles; and differential pressure indicating means for indicating the difference of liquid pressure in said portions of said conduits, the improvement which comprises: a. second pump means communicating with said source and with each of said conduits for withdrawing a stream of said suspension from said source and for feeding respective parts of said stream to said conduits under a pressure sufficient to cause flow of said parts in said conduits and outward of said nozzles into said container; and b. filter means arranged in series with said second pump means between said source and said conduits for removing said solid from said stream before said parts are fed to said conduits.
 1. In an apparatus for measuring the specific gravity of a suspension of a solid in a continuous liquid phase as a measure of the concentration of said solid in said suspension, the apparatus including a container having an inlet and two outlets communicating with the ambient atmosphere; two restricted nozzles vertically spaced in said container from said inlet in opposite vertical directions in the normal operating condition of the apparatus, said outlets being spaced from respective ones of said nozzles in a direction away from said inlet; a source of said suspension; first pump means for driving said suspension from said source into said container through said inlet and out of said container through said outlets; pressure holding means for holding the pressure of said suspension between said nozzles at least ten pounds per square inch higher than the pressure of said atmosphere when said suspension is driven into said container by said pump means; two conduits respectively communicating with said nozzles and having respective portions spaced from said nozzles; and differential pressure indicating means for indicating the difference of liquid pressure in said portions of said conduits, the improvement which comprises: a. second pump means communicating with said source and with each of said conduits for withdrawing a stream of said suspension from said source and for feeding respective parts of said stream to said conduits under a pressure sufficient to cause flow of said parts in said conduits and outward of said nozzles into said container; and b. filter means arranged in series with said second pump means between said source and said conduits for removing said solid from said stream before said parts are fed to said conduits.
 2. In an apparatus as set forth in claim 1, each of said conduits having a vertical portion, said portions jointly extending over substantially the entire vertical spacing of said nozzles and being connected to a vertically coextensive portion of said container for heat exchange between fluid in said conduit portions and corresponding portions of said suspension in said container, feeding tubes connecting said second pump means to respective vertically contiguous parts of said conduit portions, said feeding tubes respectively having sections extending from said parts horizontally in heat transmitting engagement with said container toward said second pump means.
 3. In an apparatus as set forth in claim 2, said container being tubular, and said sections of said feeding tubes being coiled about said tubular container. 